At Advertising Week, Google today introduced a new ad format called Lightbox, which is a standard ad unit that expands into a super-sized canvas takeover ad after a user hovers their mouse cursor over the ad. The company says that the ad will offer advertisers a way to pay only for engaged users, as advertisers will only pay when the ad is expanded, as opposed to clicked. For users, the ad is designed to minimize accidental expansions, as it requires the user to hover their mouse over the ad for two full seconds before the expansion occurs.

Google says it has tested the ad format internally, and found that the smart hover feature, as it’s being called, eliminated nearly 100% of accidental expansions and increased engagement by 6 to 8 times over standard click-to-expand ads. The new ads can include a variety of content, including rich media like YouTube videos, a game, photos, a shopping experience, and more. The ads will be available for advertisers to run online, but a Google spokesperson told us that they’re working on extending the format to mobile.

The company also said it’s now working with a handful of advertisers on the unit, but declined to provide details as to which companies have the unit in testing. Other advertisers aren’t able to launch their own Lightbox format ads yet, but the spokesperson said these units will be rolling out “soon.”

The Lightbox ad is the first in a new family of display ads that will allow advertisers to only pay when a user engages, says Google on a company blog post announcing the addition. The post also provided some details on Google’s TrueView family of video ads, which are similarly focused on giving users more control over the video ads they see, also with the goal of offering better engagement metrics to advertisers. The company says it looked the sales impact during two weeks after 92 different ad campaigns, and found that on average, every $1 invested delivered a $1.70 return in sales – that’s 2.4x more efficient than TV ad spend, Google proclaimed. On average, YouTube and Google Display Network ads drove a 36% increase to website visits and a 36% increase in searches for the advertiser’s brand online, according to Google’s internal data.